Hydroconversion of hydrocarbons



United States Patent US. Cl. 208-110 9 Claims ABSTRACT OF THE DISCLOSUREHydrocracking catalysts which have been partially deactivated bypolycyclic aromatic hydrocarbons present in the charge stock arereactivated by introducing a feed having a lower polycyclic aromaticcontent.

This invention relates to the conversion of hydrocarbons. Moreparticularly it is concerned with the conversion of hydrocarbons in thepresence of hydrogen to lighter hydrocarbons. In its most specificaspects it is concerned with the conversion of hydrocarbon feed stocksboiling approximately in the kerosine-gas oil range in the presence ofhydrogen and a cracking catalyst into hydrocarbons boiling in thenaphtha-kerosine range.

Hydrocracking, previously known as destructive hydrogenation, has comeinto prominence recently in the refining of petroleum hydrocarbons. Inthe hydrocracking process various reactions take place such as thecleaving of long straight carbon chains, the saturation of aromaticrings with subsequent rupture of cycloparafiinic structure, theisomerization of parafiinic chains into isoparaffinic chains and thedealkylation of alkyl aromatics. Ordinarily, the charge to ahydrocracking unit will comprise a hydrocarbon fraction boiling abovethe boiling range of the desired product. For example, if a motor fuelis desired, the charge to the hydrocracking unit will generally have aninitial boiling point of about 400-450 F. whereas if the desiredproducts are motor fuels and jet fuels, then the charge to thehydrocracking unit will generally have an initial boiling point of about550'600 F. Advantageously, charge stocks such as straight run kerosineand gas oil stocks from catalytic cracking, vacuum gas oil and lightdistillates obtained from coal and shale may be charged to thehydrocracking unit. Ordinarily, product boiling above the desired endpoint is recycled to the hydrocracking unit.

Hydrocracking is preferably carried out in the presence of a catalystwhich contains two components, a hydrogenating component and a crackingcomponent. Numerous hydrogenating components such as Group VIII metals,for example platinum, palladium and nickel and the oxides and sulfidesof molybdenum, nickel, copper, tungsten, and cobalt, and the like ormixtures thereof, have been disclosed in the prior art. Thehydrogenating component is supported on a cracking base whichadvantageously is acidic in nature. Such bases comprise refractoryoxides of two or more elements of Groups II, III, and IV of the PeriodicTable. Suitable cracking supports include silica-magnesia,silica-alumina, silica-alumina-zirconia and the like. Preferably thecracking support is a crystalline alumino-silicate of the natural orsynthetic zeolite type having uniform pore openings of 6-14 angstromunits.

While these catalysts are eminently suitable for the hydrocracking ofvarious petroleum charge stocks, they are subject to a loss of activityas the reaction proceeds. As a measure of the catalyst activity it iscustomary to institute a hydrocracking reaction and to conduct theprocess at certain conditions of temperature, pressure, space velocityand hydrogen circulation rate to maintain a pre- 3,436,338 Patented Apr.1, 1969 determined conversion of the charge into material having aparticular end boiling point. As the reaction is continued, the catalystis subject to loss in activity and to compensate for the reducedactivity the temperature in the catalytic zone is increased to maintaina constant conversion rate. This increase in temperature necessary tomaintain the desired amount of conversion is called the aging rate. Forconvenience, the aging rate is measured in F./ hours, that is, thenumber of F. the catalyst bed temperature must be increased per 100hours to maintain a constant rate of conversion.

In commercial operation, it has been found uneconornh cal to extend theon-strearn production step beyond a catalyst bed temperature of about775 F. At this stage the aging rate of the catalyst becomes so rapidthat it has been deemed advisable to terminate the production step andto regenerate the catalyst. The inactivity of the catalyst when thistemperature has been reached is usually due either to poisoning by thenitrogen in the charge stock or to the deposition of coke or carbon onthe cata lyst or a combination of both. In any event, the catalyst isregenerated by oxidative combustion.

Oxidative regeneration is a costly procedure in that first it requiresthe termination of the flow of reactants to the reaction zone andpurging of combustible materials from the system by sweeping with aninert gas. Oxygen diluted to a very low concentration by an inert gassuch as nitrogen is then introduced into the reactor and the temperatureis very carefully controlled to prevent overheating of the catalyst bythe combustion of the deposited coke. When all of the coke has beenremoved by oxidation, the system is then again swept by an inert gas toremove all of the oxygen and when this has been effected the productionstep is reinstituted. This procedure is not only costly in itself, butalso in the fact that it requires that the unit be shut down in someinstances for as much as one week.

By the process of the present invention, the aging rate of a partiallydeactivated catalyst can be reduced and its conversion can be improvedby charging to the catalyst a hydrocarbon feed stock of reducedpolycyclic aromatic content. It has now been found that an increase inthe polycyclic aromatic content of the charge results in a correspondingincrease in the aging rate of the catalyst and that a decrease in thepolycyclic aromatic content of the charge not only results in a decreasein the aging rate but also restores the catalyst to its initialconversion activity prior to the introduction of the charge stock ofhigher polycyclic aromatic content. This latter is evidenced by the factthat the same conversion rate can be obtained at a considerably reducedtemperature.

The catalysts used in the hydrocracking process of the present inventioncomprise a hydrogenating component such as a Group VIII metal or metalcompound such as platinum, palladium, nickel and the oxides of nickeland cobalt alone or in conjunction with compounds of molybdenum ortungsten. The hydrogenating component is supported on a crackingcomponent comprising a refractory oxide such as alumina, magnesia,silica and the like and mixtures thereof. Particularly suitable crackingcomponents comprise natural or synthetic zeolitic alumino-silicateshaving uniform pore openings in the 6l4 angstrom unit range, preferablyin the 10-14 angstrom unit range and in which the alkali metal ions havebeen replaced by hydrogen ions or divalent metal ions such as magnesium.

The hydrogen used in the present process may be suitably obtained as aby-product from catalytic reforming, by the electrolysis of water or bythe partial combustion of carbonaceous or hydrocarbonaceous material toproduce synthesis gas which is then subjected to shift conversion toproduce relatively pure hydrogen. It is not necessary in the presentprocess that the hydrogen be pure. Ordinarily, a hydrogenating gashaving only 40 volume percent hydrogen may be satisfactorily usedalthough a gas containing 8990 volume percent hydrogen is preferred. Inthis specification and in the appended claims the term hydrogen isintended to include dilute or impure hydrogen.

The reaction conditions within the hydrocracking unit generally includea temperature range from about 450- 775 F. although a temperature from500 to about 725- 750 F. is preferred. Pressure will range from aboutSOD-10,000 p.s.i.g. or higher although a pressure of from about 1,000 to3,000 p.s.i.g. is preferred. The hydrogen rate may range from 1,000 toabout 20,000 s.c.f.b. (standard cubic feet per barrel) of normallyliquid charge. Preferred hydrogen rates are from about 3,000-8,000s.c.f.-b. Preferably the space velocity, that is the volumes of liquidcharge per volume of catalyst per hour, will be between 0.5 and 3although rates ranging from 0.1- may be used.

If the charge stock to the hydrocracking unit contains not more thanabout 2-20 p.p.m. nitrogen it may be charged directly to thehydrocracking unit. Preferably as in the case of higher nitrogencontaining stocks, the hydrocarbon feed is first charged to a catalyticdenitrogenation zone where it is contacted with a catalyst such as amixture of oxides of cobalt and molybdenum generally referred to ascobalt molybdate on a support such as magnesia or alumina. Suitableother catalysts comprise the oxides or sulfides or mixtures thereof ofmetals such as nickel, molybdenum, co'balt, tungsten and the like, forexample sulfided nickel tungsten on alumina or a mixture of nickel andmolybdenum in either the oxide or the sulfide form on alumina.Satisfactory denitrogenation conditions include a temperature range of700-900 F., a pressure of 1005,000 p.s.i.g., a space velocity of 01-10,and a hydrogen rate of from 500- l0,000 s.c.f.b.

In the two-stage denitrogenation and hydrocracking operation each stagemay have its own hydrogen circulation system or the hydrogen maycirculate serially through both reaction zones. However, if the hydrogenfrom the denitrogenation Zone is to be used in the hydrocracking zoneand the hydrocracking catalyst is sensitive to ammonia, the hydrogen maybe subjected to a basic nitrogen removal treatment as for example bywashing with dilute acid and the charge to the hydrocracking unit afterremoval from the denitrogenation zone is advantageously stripped with aninert gas for the removal of nitrogen compounds such as ammoniatherefrom. Apparently, the use of molecular nitrogen as a stripping gas,even though it is retained to the extent of 100 p.p.m. in the strippedhydrocracking unit charge stock, exerts no deleterious effect on thenitrogen-sensitive hydrocracking catalyst. The denitrogenation treatmentalso effectively removes oxygen containing compounds from the charge. Ifthe hydrocracking catalyst is not sensitive to ammonia, the entireefiluent from the denitrogenation zone may be sent directly withoutintermediate treatment to the hydrocracking zone.

The improved process of our invention is particularly applicable topartially deactivated catalyst and serves to delay the time whenoxidative regeneration becomes necessary. It also permits the sameconversion to be obtained at a lower temperature. The improvement isparticularly noticeable when the charge stock has a polycyclic aromaticcontent of more than about 11 weight percent and when polycyclicaromatic content of the charge is reduced to below about 11 weightpercent.

In an example of the invention, a sulfided nickel tungsten on silicaalumina catalyst containing 5.9% nickel, 18.6% tungsten, 50.9% silicaand 17.3% alumina was used at conditions of 1500 p.s.i.g., 6000 s.c.f.hydrogen per barrel of liquid feed, 1.0 space velocity (volume of liquidcharge per volume of catalyst per hour) and temperature to obtain a 50%conversion of material boiling about 400 F. to material boiling below400 F. The following fluid catalytic cracking cycle gas oils were used.

Charge A was fed at the above conditions for a 280 hour induction periodto stabilize the catalyst. Charge B was then fed for 171 hours at whichtime feed was switched to Charge C. After 53 additional hours Charge Awas reinstituted as the feed. The temperatures for 50% conversion to 400F. material are shown below.

Deg., F. Hours on stream These data show that the aging rates after theinitial induction period are Charge B, 4.9 F./ hours; Charge C, 38F./100 hours; and Charge A, 3.5 F./l00 hours. More significant is thefact, that after Charge C had been run for 50 hours, a temperature of684 F. was required for a 50% conversion yet when Charge A was restoredas the feed, a 50% conversion was obtained at 666 P. which, at a 3.5 F.aging rate, is equivalent to extending the life of the catalyst 500hours.

Obviously, many modifications and variations of the invention ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

We claim:

1. A method for improving the activity and reducing the aging rate of ahydrocracking catalyst comprising a hydrogenating component and acracking component which has become partially deactivated in a processfor the hydrocracking of a hydrocarbon charge stock containingpolycyclic aromatic hydrocarbons which comprises bringing the catalystinto contact under hydrocracking conditions with a hydrocarbon chargestock having a polycyclic aromatic content lower than that of theoriginal hydrocarbon charge stock.

2. The process of claim 1 in which the original charge stock containsless than 5 p.p.m. nitrogen.

3. The process of claim 1 in which the original charge stock is a cyclegas oil obtained from catalytic cracking.

4. The process of claim 1 in which the catalyst comprises nickel.

5. The process of claim 4 in which the catalyst comprises sulfidednickel and tungsten.

5 6 6. The process of claim 1 in which the original charge ReferencesCited stocl contains more than about 11 weight percent poly- UNITEDSTATES PATENTS cyclic aromatic hydrocarbons.

7. The process of claim 1 in which the charge stock of 2,614,068 10/1952Healy et a1 208 78 3,158,563 11/1964 Strecker 208-111 lower polycyclicaromatic content contains less than about 11 weight ercent 01 c clicaromatic h drocarbons.

8. The p ocess of? 0131i; 1 in which the original charge D ELBERT GANTZPrlma'y Exammer' stock is subjected to a preliminary denitrogenationstep. G. E. SCHMITKONS, Assistant Examiner.

9. The process of claim 8 in which the entire efiluent from thepreliminary denitrogenation step is passed to the 10 US. Cl. X.R.

hydrocracking zone. 89

